Unlike retail, OEM's don't come with colourful boxes and detailed manuals and CD's. And like aadipa said, the license is non transferable. It's tied to the hardware it came with. I think Windows activation deletes all records after 120 days. So if you do a major hardware upgrade, you should be fine reactivating as long as the previous activation was done before 120 days.
hey i am using an OEM version of Win XP home SP2 ... i bought it separately and i am using an assembled pc .. before purchasing it i had talked with the microsoft connect people and they had assured me that OEM version can also be used if u upgrade ur hardware (without any time limit) ...they just told me i will be able to use it only on one pc at a time... is that true or not ? if i upgrade my comp will i be stuck without being able to activate it ?